I would like to systematize my U-Boot/linux knowledge. Is it true that minimum 2 bootloader phases are needed in each embedded platform? Or can following process vary?

  1. 1st-stage bootloader (can be U-Boot) is stored in internal the processor's ROM and can't be updated. It will run from internal cache memory. This U-Boot needs to (at least): initialize RAM, initialize external flash, initialize serial console, read and run 2nd-stage bootloader.

  2. 2nd-stage bootloader (can be U-Boot) is stored in RW flash memory. It will handle ethernet, flash RW functions, etc. This U-Boot can be customized and overwritten. Main task is to load linux kernel into RAM and run it.

  3. linux kernel startup.

Is 1st-stage bootloader always Read-Only?

linux embedded embedded-linux u-boot
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